Wiring through joists in an insulated floor

[wevcore]

Hello,

I'm about to start a complete house refurbishment, including rewiring and insulating between floors.

As I understand it building regs require you to drill holes through the center of joists 0.25-0.4 along the span of the joist - this is going to put my cable run ~75cm away from the wall. Joists are 180mm high - I intend on completely insulating the void between ceiling/floor.

In an ideal world, I'd like to drill my holes right next to the wall so cable passing through joists are adjacent to walls. Cables running in the direction of the joists would be supported by P-clips allowing fast & easy installation. Installing the insulation, the cables would then be touching the joist/wall and could be argued as being installation method 100/102.

With my cables ~75cm into the room, will I either have to leave an insulation gap around the cables, or install a conduit between each joist and call it method A*? Or do I notch the joists (will have to be the bottom of the joist) and can this be classed as installation method 100/102?

Do cables have to be tightly clipped to joists along their run, or is running them in P-clips and pushing them against the joists with the insulation acceptable?

What's best practice in the industry?

Any help appreciated
Thanks,
Kevin

 

[Baddegg]

I wouldn’t recommend notching the bottom of joists mate you’ll weaken em, Why do you want insulation in a floor/ceiling void?....but if you feel the need I’d run the cables as per regs and just leave a gap in (I’m assuming) rigid insulation boards??

 

[Dustydazzler]

Certainly wouldn’t be notching joists , I would install cables and just leave small gaps in the insulation so it isn’t touching

 

[SJD]

If the floor has noggins between the joists in the range 0.25 to 0.4 of the span, you can perhaps drill the joists close to the noggins and clip the cables to them?

If this is an old building, are there already holes in the joists, it is worth checking. On occasion, I've found a whole row of unused old holes through every joist. You might even find existing holes not complying with the 0.25 to 0.4 rule, but if already drilled, you can use them!

As mentioned, definitely not notching the joists on the underside.

 

[Mike Johnson]

Structural Engineers have given guide lines on how this should be done, they would not presume to tell you how to wire a CU, why would you presume to tell them where to cut holes in the joists.

 

[wevcore]

I will definitely be following the guidance and drilling my holes in the 'zone' of the joist. Unfortunately there aren't any existing - that would be great!

I'll just leave gaps in the insulation where cables pass through.

Thanks all